This U01 application seeks funds for 3 years to conduct a Phase II clinical trial that will evaluate the efficacy of the non-selective Beta-adrenergic antagonist, propranolol, compared to placebo, for treatment of pain in patients with temporomandibular disorder (TMD). TMD, one of the most common chronic musculoskeletal pain conditions, is ineffectively treated. Growing evidence suggests that pain states are enhanced by diminished activity of catechol-O-methyltransferase (COMT; an enzyme that metabolizes catecholamines), which results in elevated levels of catecholamines and increased activity of Beta 2/3-adrenergic receptors. Three common haplotypes in the COMT gene have been associated with pain modulation and the risk of developing TMD. In a pilot study of TMD patients, we found that analgesic efficacy of propranolol varied according to polymorphisms in the COMT gene. We now propose to conduct a Phase II randomized, masked, placebo-controlled, parallel assignment clinical trial of propranolol (LA 60 mg twice daily). The primary objective is to evaluate the efficacy of propranolol in reducing pain in TMD patients; a secondary objective will determine if propranolol efficacy varies according to patients' COMT diplotype. We will enroll 200 Caucasian female TMD patients, genotyped for COMT polymorphisms. This trial will consist of a 1-week baseline phase, a 10-week treatment phase, and a 1-week follow-up. The primary endpoint will be a weekly mean pain index, calculated as a product of the pain intensity score multiplied by the pain duration score from a Daily Symptom Diary. Patient pain ratings, responses to heat and pressure stimuli, physical function, emotional function, global improvement, occurrence of symptoms and adverse events, and use of rescue medication will be measured as secondary endpoints. Statistical analysis will evaluate three trial hypotheses: 1) propranolol is efficacious compared with placebo in reducing the pain index, 2) efficacy of propranolol varies according to patients' COMT polymorphism, and 3) propranolol is efficacious in improving secondary endpoints. Continuous measures will be analyzed in the intent-to-treat sample using methods for mixed-model repeated measures, with the baseline scores as covariates. Sensitivity analyses will be conducted with the per-protocol sample. Under an R34 grant, we have created the protocol, informed consent forms, the Manual of Procedures, case report forms, and study plans needed for the proposed clinical trial. The proposed study will generate new evidence about treating pain through previously unexploited pharmacologic targets (e.g., Beta-adrenergic receptors). The study offers potential for a genetically-tailored pharmacogenetic approach for TMD treatment and may explain variability of treatment responses to Beta-blockers when used to treat other diseases.